In a conventional photovoltaic power harvesting system configured to feed a single phase or a three phase alternating current (AC) power grid, dual (positive and negative) direct current (DC) power may be generated first from solar panels. The three phase inverter powered by the dual (positive and negative) DC power produces three phase AC power at the output of the three phase inverter. Conventionally, sufficiently high DC voltage may be provided to the input of the three phase inverter by connecting solar panels in series. However, in order to increase overall power conversion efficiency, the sum of positive and negative DC rails required by the inverter may be over 600 volts.
In North America, an input of voltage over 600 volts may create an issue with safety agency approval under regulation UL1741. An approach to avoid the safety issue may include inputting less than 600 volts to a boost circuit or transformer-isolated circuit to generate dual DC rails internally for the inverter input. The additional boost or transformer-isolated circuit increases cost and complexity especially since the additional power converter module generally requires dedicated control and protection features. Additionally, the boost or transformer-isolated circuit may also generate electromagnetic interference (EMI) and may cause reduction in overall efficiency of conversion of DC power to three phase AC power.
Thus there is need for and it would be advantageous to have a DC link circuit with a low voltage input, which does not cause significant reduction in overall efficiency of conversion of DC power to three phase AC power and which provides a sufficiently high DC input voltage to the AC inverter to generate an AC output of the inverter of required magnitude.